1. Field of the Invention
The present invention relates to a liquid crystal display unit used in a display device such as a computer, a television receiver, and many others.
2. Description of the Related Art
In a liquid crystal unit used as a television that reproduces moving image, demands for image quality, including a moving image response performance and a contrast, are high. A display unit that tightly holds a negative dielectric anisotropic liquid crystal layer between the substrates opposed to each other and that employs a liquid crystal display panel in which liquid crystal molecules are almost vertically oriented to the substrates when voltage is not applied to the liquid crystal molecules is characterized by its high contrast and high-speed response performance. However, the display unit has a problem of poor display quality. Specifically, because of the high dependency on a viewing angle, transmittance in an oblique direction becomes higher than the one in a vertical direction when watched from an oblique direction, and therefore its tone becomes larger than a desired tone (appears whitish).
This is caused especially by increase of transmittance in an intermediate tone display, in a direction in which a displacement direction of the obliquely inclining liquid crystal molecules is identical with the direction of diffused transmitted light from a back-light.
In this connection, Japanese Patent Application Publication No. 2002-372713 (published on Dec. 26, 2002) suggests a liquid crystal display unit employing a back-light that outputs parallel light to a liquid crystal display panel. The liquid crystal display unit having a high quality display can be achieved by employing a back-light that outputs parallel light so as not to depend on displacement direction of the liquid crystal molecules and so as not to depend on a viewing angle (off tone in certain viewing directions) in a case of an intermediate tone display.
However, currently, it is practically difficult for a back-light to output perfectly parallel light. Besides, even if a back-light can output perfectly parallel light, the cost is so high that it is impractical. Accordingly, the liquid crystal display unit disclosed in Japanese Patent Application Publication No. 2002-372713 has a problem that a whitish appearance (a tone higher than a desired tone) occurs when parallel light output from a back-light is not perfectly parallel.
Generally, for the purpose of increasing a viewing angle, a scattering sheet is disposed in front of a liquid crystal display panel. This scattering sheet is for scattering light to all directions, regardless of the incident angle, e.g. in a front direction and an oblique direction. Light entering the liquid crystal display panel and then entering the scattering sheet disposed in front of the panel is scattered to all directions by this scattering sheet. Because light output in a front direction of the liquid crystal display panel is scattered to all directions, a viewer can observe the light output in the front direction of the liquid crystal display panel, not only in the front direction but also in an oblique direction off to leftward/rightward/upward/downward.
However, this scattering sheet also evenly scatters light, which is output in an oblique direction, to all directions. Therefore, light obliquely going through the liquid crystal display panel can be watched from a wide range of angles. Therefore, the liquid crystal display unit disclosed in Japanese Patent Application Publication No. 2002-372713 has a problem of generating a whitish appearance.